1. Field of the Invention
The present invention relates to a focusing method, and more particularly to a continuous focusing method for determining whether to adjust a focusing focal length or not when a digital camera is switching scenes.
2. Related Art
A user usually takes a picture with a digital camera in the following several stages. First, the digital camera is turned on; at this time, the digital camera enters a live view stage. Second, the user half presses a shutter after aiming at an object to be shot, and at the same time, the digital camera enters an auto focusing stage. Third, the user fully presses the shutter, and at this time, the digital camera enters a shooting stage.
The so-called live view stage means previewing scenes with the digital camera before the user presses the shutter. In other words, the digital camera continuously captures different scene pictures during the live view stage and displays the image pictures on a liquid crystal display of the digital camera. At this time, the digital camera continues auto focusing on the scenes, thereby adjusting the lens to suitable focusing positions. In such a manner, the estimation duration for subsequent focusing may be decreased.
In the auto focusing stage, the digital camera starts to adjust a focal length between a lens assembly and an object to be shot in the scene after the user half-presses the shutter. At this time, a focusing object of the digital camera is the object to be shot. Therefore, the digital camera may adjust the focal length for the object to be shot once again. The shooting stage means that the digital camera records a current image picture as a digital image when the user fully presses the shutter.
Taking the continuous focusing procedures during the live view stage as an example, the digital camera performs comparison calculation on a plurality of continuous images. When a lens position of the digital camera is at a different position, the digital camera obtains a contrast value for the definition of each image. Next, the digital camera obtains an optimal focusing focal length through a quadratic curve approximation manner according to a relation between the contrast value and the focal length. However, when the digital camera switches scenes, the lens keeps performing zooming out/in motions. As a result, not only the focusing duration of the digital camera is prolonged, but also the power consumption of the digital camera is severely increased.